The invention relates to torque transmitting apparatus, and more particularly to improvements in apparatus for transmitting torque between the output element of the internal combustion engine and the input element of the change-speed transmission in a motor vehicle. Still more particularly, the invention relates to improvements in torque transmitting apparatus of the type wherein a slip friction clutch is installed between a set of flywheels one of which can be driven by the engine and the other of which can drive the change-speed transmission of a passenger car or another motor vehicle.
U.S. Pat. No. 4,274,524 to Nakane discloses a rotational torque transmission mechanism wherein the angular movements of one flywheel relative to another flywheel are opposed by a slip clutch and a damper in series with the slip clutch. The damper comprises a set of coil springs which operate in parallel with a friction generating device. Torque which is transmitted by the slip clutch greatly exceeds the maximum nominal torque which is generated by the internal combustion engine i.e., the slip clutch reacts only in response to highly pronounced fluctuations of torque.
The patented mechanism is capable of reducing the stress upon the power train between the engine and the wheels of the vehicle, and such mechanism is also capable of enhancing the comfort of the passenger or passengers and of effecting a certain reduction of noise. This is attributable to the ability of the mechanism to reduce shocks which often develop at low rotational speeds when the vehicle travels at a low speed, i.e., to the ability of the mechanism to allow for oscillation of the vehicle in the direction of travel. However, the patented mechanism fails to operate satisfactorily under numerous other circumstances which arise when a motor vehicle is in use, particularly within the full RPM range of the engine. The main reason is that, as mentioned above, torque which can be transmitted by the slip clutch of the mechanism of Nakane must considerably exceed the torque which is transmitted by the engine because the mechanism is designed to take into account tolerances in the making of discrete parts as well as that torque which is transmitted by the slip clutch is likely to vary under different operating conditions and on prolonged use of the vehicle. It has been found that the prestressing of the diaphragm spring which is used in the patented mechanism is likely to change with progressing wear upon the friction linings. Moreover, the coefficient of friction is likely to change within a wide range, for example, as a result of overheating and/or as a result of contact with a lubricant. The slip clutch transmits a substantial torque even when the engine operates in the lower RPM range, i.e., when the magnitude of engine torque is relatively low. This is particularly undesirable during starting or stoppage of the engine when the operation takes place at the critical frequency at which resonance is likely to develop. The result is extensive wear upon the parts and the development of undesirable noises.